1. Field of the Invention
This invention relates generally to turbocharger shaft seal arrangements. More particularly, a pressure balanced dual piston ring configuration on the shaft in combination with a compression seal engaged between the center housing and turbine wheel shroud provides an effective turbine end seal for avoiding contamination by condensates and vapor in the exhaust gas driving the turbine.
2. Description of the Related Art
Turbochargers are being employed in numerous applications including conventional internal combustion engine charge air boosting and new concepts for turbopumping of exhaust gases and pressurizing reactants for power generation systems such as fuel cells. In most turbochargers operational requirements dictate the need for relatively leak-free seals between the shaft bearings within the center housing, and the rotating turbine and compressor wheels. This is particularly true at the turbine end of the shaft, since the turbine typically operates in a relatively high temperature environment. Accordingly, it is desirable to prevent leakage of bearing lubricant into the turbine housing to prevent gumming or coking of the lubricant in high temperature applications, which can detrimentally affect the turbine performance and further to prevent partial ignition of the lubricant within the turbine housing or blow through of the lubricant, either of which creates adverse effects on the level of pollutants discharged by the system. Similarly, avoiding contamination of the inlet compression gas stream by lubricant from the center housing is important.
In many applications, the requirement exists for significantly reduced contamination of the compression gas stream over the available art and avoiding contamination of the turbocharger lubricating oil by water vapor, condensates or other corrosive effluents in the exhaust gas stream driving the turbine of the turbocharger. The prior art typically employs one or more sealing rings on the turbine shaft in a labyrinth arrangement for preventing leakage on one or both the turbine and compressor sides of the shaft. Additionally, venting the compressor end seal within the center housing to allow lubricant contacting the seal to drain and slinger arrangements on the shaft for pumping excess lubricant radially away from the seal rings are employed for increasing, efficiency of the overall seal configuration. These prior art configurations, singly and in various combinations have not demonstrated sufficient sealing capability for new high efficiency sealing requirements.
The present invention provides increased sealing effectiveness over the prior art by combining plural sealing elements with an integral pressure balancing cavity receiving pressurizing gas from the compressed gas stream or an external source.